We have previously demonstrated in cats that treadmill exercise training does not result in alteration of basic contractile state of the myocardium. Additionl studies have demonstrated that pulmonary artery constriction with a 4.0 mm (I.D.) clip in adult cats results in a 30% incidence of deaths from congestive heart failure and depressed right ventricular papillary muscle mechanics 6 weeks after banding. The proposed studies will determine whether exercise conditioning has a beneficial effect on the myocardial response to pulmonary artery constricition. Cats will undergo artery constriction after they have been exercised to the point of a training effect. Mortality from heart failure and papillary muscle mechanics 6 weeks after banding will be compared to those of non-exercised banded animals. Additional studies will be devoted to the development of a new model of pressure-induced myocardial hypertrophy in which the pressure load is gradually applied. The cross-sectional area of the pulmonary artery will be reduced by 50 to 60% and right ventricular systolic pressure elevated 5 to 10 mm Hg by an appropriate size clip placed around the pulmonary artery of kittens at the time they attain a weight of 1 kg. Animals will be sacrificed at 1,2,4,6, and 12 months after banding and hemodynamics, right ventricular mass and right ventricular papillary muscle mechanics determined. BIBLIOGRAPHIC REFERENCES: Williams, J.F., Jr. and Potter, R.D. The Effect of Chronic Digitoxin Administration on the Contractile State of Normal and Nonfailing Hypertrophied Myocardium. Journal of Clinical Investigation. 56:71-78, 1975.